System and method for Microablation of tissue

ABSTRACT

The present invention generally relates to the field of laser treatment of tissue, and particularly, to a system and method for creating microablated channels in skin. The present invention is more particularly directed to treating subsurface tissue through the created channels.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 11/730,017 filed Mar. 29, 2007, which claims priority to U.S.Ser. No. 60/791,194, filed on Apr. 12, 2006, U.S. Ser. No. 60/850,628,filed on Oct. 11, 2006, and U.S. Ser. No. 60/832,964, filed on Jul. 25,2006. These applications are incorporated by reference in theirentireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to the field of laser treatmentof tissue, and particularly, to a system and method for creatingmicroablated channels in skin. The present invention is moreparticularly directed to treating subsurface tissue through the createdchannels. By doing treating subsurface tissue through uniquely createdchannels, skin may be treated with heretofore unrealized results.

2. Description of the Related Art

Skin is primarily made of an outer layer, or epidermis, that has a depthof approximately 100/an from the outer surface of the skin and an innerlayer, or dermis, that has depth of approximately 3000 fm from the outersurface of the skin. As used herein, “dermal tissue” or “skin” refers toboth the dermis and epidermis layers.

There is ongoing demand for procedures to improve skin defects. Suchimprovements include reducing wrinkles, reducing dyschromia (a varietyof abnormalities or irregularities of skin color resulting from, interalia, irregular pigment distribution, dilated blood vessels, etc.) andetc. A wide variety of skin treating techniques have been introduced inrecent years for attempting to achieve this objective. The skin treatingtechniques that have been employed may be generally categorized into twogeneral types of treatment: ablative laser skin resurfacing (“LSR”) andnon-ablative collagen remodeling (“NCR”). LSR generally may result infairly extensive thermal damage to either the epidermis and/or thedermis. NCR, on the other hand, is designed to avoid thermal damage ofthe epidermis.

Nevertheless, LSR is an effective laser treatment for treating skin. Atypical LSR procedure comprises thermally damaging a region of theepidermis 100 and a corresponding lower region of the dermis 110 forpromoting wound healing. Electromagnetic energy 120 is directed towardsa region of skin, thereby ablating the skin and removing both epidermaltissue and dermal tissue. Combining LSR with a pulsed laser, for examplea CO₂ or an Er:YAG laser, is typically referred to as laser resurfacingor ablative resurfacing. This is considered to be an effective treatmentprotocol photo aged or chronically aged skin, scars, superficialpigmented lesions, stretch marks, and/or superficial skin lesions. Majordrawbacks include, however, edema, oozing, and burning discomfort up tothe first fourteen (14) days after treatment. Such drawbacks areunacceptable for many patients. A further problem with LSR procedures isthat they are relatively painful. Therefore, they generally require anapplication of a significant amount of analgesia. While LSR ofrelatively small areas can be performed under local anesthesia, LSRprocedures that include relatively large areas frequently requiregeneral anesthesia or nerve blockage by multiple anesthetic injections.

Another limitation of LSR is that ablative laser resurfacing generallycannot be performed on the patients having dark complexions. Ablation ofpigmented epidermis tissue can cause severe cosmetic disfigurement topatients having a dark complexion. Such disfigurement can last fromseveral weeks up to years. This is generally considered to beunacceptable by most patients and physicians. Yet another limitation ofLSR is that ablative resurfacing generally has a greater risk ofscarring in areas other than the face and result in an increasedincidence of an unacceptable scar formation because the recovery fromskin injury within these areas is not very effective.

Several NCR techniques have attempted to overcome the aforesaid problemsassociated with LSR procedures. These techniques may be variouslyreferred to as non-ablative resurfacing, non-ablative subsurfacing, ornon-ablative skin remodeling. Such NCR techniques generally usenon-ablative lasers, flash lamps, or radio frequency current fordamaging the dermal tissue and avoiding damage to the epidermal tissue.NCR techniques apply the concept that it is the thermal damage of thedermal tissues that is thought to induce wound healing. This results inbiological repair and the formation of new dermal collagen which in turncan result in decreased photoaging related structural damage. Avoidingthe epidermal damage by using NCR techniques may also decrease both theseverity and the duration of treatment related side effects, forexample, post procedural oozing, crusting, pigment changes, and theincidence of infections.

Treating skin using the NCR method involves heating selective portionsof dermal tissue within the dermal layer for inducing wound healingwithout damaging the epidermis above. By cooling the surface of the skinand focusing electromagnetic energy, for example a laser beam, aselected dermal damaged region can be achieved while leaving theepidermis undamaged. Using non-ablative lasers for damaging the dermiswhile leaving the epidermis undamaged is common to NCR treatmentmethods. Generally, using non-ablative lasers result in deeper dermalpenetration depths as compared to the ablative lasers than thesuperficially-absorbed ablative Er:YAG and CO₂ lasers used in typicalLSR procedures. Further, when NCR techniques are used, they generally donot have the undesirable side effects characteristic of the LSRtreatment, such as the risk of scarring or infection. Examples of NCRtechniques and apparatus are disclosed by Anderson et al. in U.S. PatentPublication No. 2002/0161357.

Although these NCR techniques may avoid epidermal damage, a majordrawback of this method is its limited effectiveness. For example, thisis significantly less improvement of photoaged skin or scars after theNCR treatment than when LSR ablative techniques is used. In fact, evenwhen multiple NCR treatments are employed, improvement in the patient'sskin is often far below expectations. In addition, improvement is oftendelayed for several months when a series of treatment procedures areused. Although NCR techniques have been found to be moderately effectivefor wrinkle removal, they have generally not been found to be effectivefor dyschromia.

Another problem with using a NCR technique is the limited the breadth ofacceptable treatment parameters for safe and effective treatment ofdermatological disorders. This is because NCR procedures generally relyon an optimum coordination of laser energy and cooling parameters. Thisresults in an unfavorable temperature profile in the skin. Anunfavorable temperature profile consequently results in either notherapeutic effect on one hand, or scar formation due to the overheatingof a relatively large volume of the tissue, on the other.

A problem that is common to both ablative and non-ablative resurfacingprocedures is that they do not significantly use keratinocytes, whichplay an active role in the wound healing response. Keratinocytes releasecytokines when the keratinocyte is damaged. Cytokines encourage woundhealing. For example, during ablative resurfacing procedures,keratinocytes are removed from the skin along with the epidermis. Thisremoves keratinocytes entirely from the healing process altogether.During non-ablative procedures, keratinocytes, located in the epidermis,are not damaged at all and thus do not release cytokines for aiding thehealing process.

Accordingly, there is now provided with this invention an improvedsystem and method for treating skin that effectively overcomes theaforementioned difficulties and longstanding problems inherent in usingeither a LSR or a NCR procedure. These problems have been solved in asimple, convenient, and highly effective way by which to treat skin.

SUMMARY OF THE INVENTION

In one aspect, the invention provides a method for treating tissue usinga laser system with pulsed light output comprising indicating by a userat least two of: (i) a desired total light output energy, (ii) a desiredaverage light output power, or (iii) a desired duration of laserapplication. The method further includes controlling the laser by thesystem in order to achieve the selected conditions (i), (ii), or (iii)specified by the user, and directing the light output of the laser tothe tissue to be treated over the desired duration.

Implementations of the invention may include one or more of thefollowing features. The laser system has a control for power that may beused to produce a population inversion, wherein the control variesbetween on and off states, and a population inversion may be producedwhen the control is varied from an off state to an on state. The systemmay vary this control between on and off states at least four times inorder to achieve the selected conditions (i), (ii), or (iii). The layersystem may have at least two attenuating elements and the system mayplace at least one of these at least two attenuating elements in thepath of the laser's output in order to achieve the desired energy oraverage power or duration.

Implementations of the invention may also include one or more of thefollowing features. The light output of the laser may be ablative duringa portion of the time that it is directed to the tissue and non-ablativeduring another portion of the time that it is directed to the tissue.Light output of the laser may be directed to the tissue through amirror, an optical fiber, a prism, or another optical element. As aresult of the light output power being directed to tissue, a channel maybe ablated in the tissue having a predetermined width and predeterminedheight. A thermal affected zone of predetermined volume and shape may becreated proximate said channel. The tissue may have a surface throughwhich the light output power passes and the thermal affected zone mayhave a cross section in a plane parallel to that surface, whichincreases in diameter with the plane's distance from that surface, suchthat, the diameter of the cross section increases with distance fromthat surface for a range of distances to the surface.

Implementations of the invention may further include one or more of thefollowing features. The method may further comprise administering atreatment through the channel. The output light power may raise thetemperature of at least a portion of the tissue into which it isdirected above 100° C. The system may measure the laser's light outputpower. The measured light output power may be used in a feedback controlsystem in order to decide when to change the control from an on state toan off state or vice versa. The desired average light output power maybe no greater than about 10% of the maximum instantaneous light outputpower which the laser is capable of producing. The light output powermay deviate by no more than 10% from the desired average light outputpower during at least about 90% of the time that the laser is producinglight output in response to the user's setting. The system may selectfrom a set of discrete attenuation values the attenuation closest to thedesired level.

In another aspect, the invention provides a system for treating tissuewith light comprising a laser with pulsed light output and a digitalcontroller for the laser. The digital controller implements a userinterface which permits a user to select at least two of: (i) a totalenergy to be applied to the tissue, and (ii) a duration of theapplication of light to the tissue, and (iii) a desired average powerlevel to be applied to the tissue. The digital controller controls thelaser's light output to achieve the conditions (i), (ii), or (iii)specified by the user. Implementations of the invention may include oneor more of the following features. The light with which the tissue istreated may have a wavelength of at least about 9 μm. The laser may becapable of producing a pulsed light output with at least about 200 Wpeak light power.

In further aspect, the invention provides a system for treating tissuewith light comprising a laser with pulsed light output, an opticalsystem for directing the light output of the laser to the tissue, and adigital controller for the laser. The laser comprises a pumpingmechanism and a control for that mechanism which can be varied betweenan on state and an off state. Varying the control from the off state tothe on state may produce a population inversion. The digital controlleris programmed to vary the control from the off state to the on state andback to the off state a plurality of times. The light output power ofthe laser does not fall to zero between the first transition to the offstate and the last transition to the on state.

Implementations of the invention may include one or more of thefollowing features. The digital controller may be programmed to receivefrom a user at least one numerical value and to compute from the atleast one numerical value a desired light output power. The averagelight output power of the laser between the first transition to the offstate and the last transition to the on state may lie within about 10%of the desired light output power.

According to one aspect of the invention, a method for treating tissueis disclosed. The method comprises applying electromagnetic radiation tothe tissue for ablating a channel therein having a predetermined widthand predetermined depth. The method includes non-ablatively heatingtissue on the bottom of the channel with electromagnetic radiation andcreating a thermal affected zone of predetermined volume proximate saidchannel.

According to another aspect of the invention, a system for treatingtissue, is disclosed which comprises an electromagnetic radiation sourceand an electromagnetic radiation emitting device for applying theelectromagnetic radiation to the tissue for forming a channel thereinhaving a predetermined width, predetermined depth, and a thermalaffected zone of predetermined volume proximate said channel.

As will be appreciated by those persons skilled in the art, a majoradvantage provided by the present invention is full control of: depth oftreatment, the amount and placement of heat, and the amount andplacement of channels. It is therefore an object of the presentinvention to rejuvenate skin and reduce wrinkles, scars, dyschromia andother conditions such as melasma and hyperpigmentation. It is anotherobject to provide a channel with or without heat for delivery othertherapy (vitamins, drugs, etc). Additional objects of the presentinvention will become apparent from the following description.

In a further aspect of the invention, a method for treating tissue usinga laser system with pulsed light output is provided. In this method, auser indicates at least two of a desired total light output energy, adesired average light output power, or a desired duration of laserapplication. The system controls the laser in order achieve the selectedconditions specified by the user and directs the light output of thelaser to the tissue to be treated over the desired duration. The systemmay achieve the conditions with the aid of attenuating elements which itcan place in the path of the laser's light output. Alternatively, thesystem may achieve the conditions by repeatedly turning on and off thepower in the laser's pumping system, causing the laser's light outputpower to be maintained in the vicinity of a specified level.

The method and apparatus of the present invention will be betterunderstood by reference to the following detailed discussion of specificembodiments and the attached figures which illustrate and exemplify suchembodiments.

BRIEF DESCRIPTION OF THE FIGURES

The patent or application file contains at least one color photograph.Copies of this patent or patent application with color photograph(s)will be provided by the Office upon request and payment of the necessaryfee.

A specific embodiment of the present invention will be described withreference to the following drawings, wherein:

FIG. 1 is a schematic illustration of a microablation method and systemin accordance with an embodiment of the invention;

FIGS. 2A, 2B, 2C, and 2D are schematic illustrations of sequentialstages of microablation and treatment in accordance with an embodimentof the invention;

FIGS. 3A, 3B, 3C, and 3D are schematic illustrations of sequentialstages of microablation in accordance with an embodiment of theinvention;

FIGS. 4A, 4B, 4C, and 4D are schematic illustrations of tissuemanipulation in accordance with an embodiment of the invention;

FIG. 5 is a schematic illustration of tissue treatment according to anembodiment of the invention;

FIG. 6 is a schematic flow chart of a method of producing microablationon a tissue in accordance with an embodiment of the invention; and

FIG. 7 is a schematic flow chart of a method of producing microablationon a tissue in accordance with an embodiment of the invention.

FIG. 8 depicts exemplary optical power output versus time curve for alaser system having pulsed output which is useful in microablation;

FIG. 9 depicts schematically a way to control optical output power of alaser by turning the pumping system power on and off;

FIG. 10 depicts schematically the use of pumping system power control toapply initially the normal high power pulse of optical energy which thelaser natively produces, followed by a selected period of sub-ablationenergy;

FIGS. 11A-11C depict schematically various attenuator arrangements;

FIGS. 12A-12F depict graphical representations of laser waveforms;

FIG. 13 is a color photograph of an irradiated polyacrylamide gel usingvarying laser pulse duration and power; and

FIG. 14 is a flow diagram of a method of treating skin using a lasersystem with pulsed light output.

DETAILED DESCRIPTION OF THE INVENTION

The following preferred embodiment as exemplified by the drawings isillustrative of the invention and is not intended to limit the inventionas encompassed by the claims of this application. A system and methodfor treating skin is disclosed herein. In skin tissue, for example,proteins such as collagen reside in the dermal layer of the skin. Themicrochannel disclosed in an embodiment of the present invention mayitself target and alter the collagen fibers within the dermis as aneffective treatment for wrinkles of the skin.

Alternatively, an embodiment of the microchannel disclosed herein maycreate a passage through which targeted tissue is treated.

As shown generally in FIG. 1, an embodiment of the present inventionprovides a system and method for performing microscopic ablation orpartial microablation of e.g. tissue, and forming a microchannel througha surface of tissue to treat subsurface tissue. The microchannel mayprovide access to subsurface tissue targeted for a prescribed treatment,or the microchannel itself may provide a prescribed treatment. In someembodiments of the present invention, the microchannel may producepartial lateral denaturation of proteins (e.g.

collagen) within the walls and/or at the bottom of the channel.

According to some embodiments of the invention, a tissue ablation system1 may include a laser unit 2 and a laser emitting device 3 for ablatinga microchannel 6 into a tissue 5, for example, for applying a treatmentthereto as will be described below in detail. The microchannel 6 may be,e.g. a column, a well, a hole, or the like, created in the tissue 5 byablating the tissue 5 by the laser emitting device 3 and the laser beam4, for example, an ablating laser beam. Microablation of the tissue 5may result in ablation of the microchannel. Microablation of the tissuemay also result in dissipation of heat from the heated and evaporatedtissue by the tissue surrounding the resultant microchannel 6. Thus,ablation of the tissue 5, producing the microchannel 6, may result in athermal affected zone 7 surrounding the walls and/or bottom of themicrochannel 6. The thermal affected zone 7 is generally indicative ofdamaged tissue and of tissue necrosis (the death of cells) inparticular. As used herein, “damaged” is defined as inducing cell deathin one or more regions of the dermal tissue of interest (“lethaldamage”), or stimulating the release of cytokines, heat shock proteins,and other wound healing factors without stimulating necrotic cell death(“sublethal damage”).

Selection of the laser beam 4 may also be based on the absorptivequalities of the tissue 5 to be treated. The absorptive properties ofthe tissue 5 to be treated may dictate or influence specific the type oflaser or the characteristics of that laser suitable for a particulartreatment for and/or microchannel. For example, certain lasers may reachdepths unable to be reached by other types of lasers. As an example, anablative laser may reach up to any depth required while non-ablativelasers may be unable to penetrate skin below, for example, about 50 μm.Similarly, it may be difficult to reach energy doses with one type oflaser that are easily reached with others. Of course, as is well knownin the art, if the wavelength is altered, the corresponding absorptionlevel of the skin treatment area will be altered. Therefore, as long asthe fluence described herein is maintained for achieving themicroablation disclosed herein, different lasers having differentcharacteristics may be used for achieving the same or similar resultsdisclosed.

The microchannel 6 may be characterized by certain parameters, forexample, diameter D and depth h. The diameter D of the microchannel andthe depth h of the microchannel generally may be controlled by theenergy characteristics of the laser. Such energy characteristicsinclude, for example, wavelength, power, and the beam profile of thelaser. Characteristics of the beam profile of the laser include, forexample, pulse width, pulse duration, and pulse frequency). Furthermore,the profile and volume of the thermal affected zone may be formed byusing different laser beam characteristics, such as chosen wavelength,energy of individual pulse or defined sequence of pulses, duration ofeach pulse, power distribution, shape of the laser spot, and the like,as will be outlined in detail below. In some embodiments of theinvention, the diameter of the ablated microchannel 6 may range fromabout 10 μm to about 500 μm, preferably in the range from about 50 μm toabout 250 μm. Microchannel diameter D may depend on the type of laserused and other parameters, for example, the elasticity of the skin. Ithas been found that the bottom of the formed microchannel is oftenconical due to the elastic forces of the skin as well as the powerenergy distribution of the spot formed by the laser.

The depth of the microchannel may be determined by the attendingphysician based upon the treatment required or selected by thephysician. For example, treatment of collagen (collagen remodeling)typically located at a depth in the range from about 200 μm to about 2mm from the surface of skin tissue may be desired. Treatment of bloodvessels may necessitate a microchannel extending up to approximately 0.5mm, which is where blood vessels are typically located. The microchannel6 may therefore be created in accordance with an embodiment of thisinvention to a predetermined depth h to effect treatment to collagen orblood vessels or any other portion of the dermis selected by theattending physician. According to some embodiments of the presentinvention, the laser device 4 may produce the microchannel 6 reaching,for example, in the range from about 100 μm to about 3 mm in depth belowthe surface of the tissue 5.

Any suitable type of laser may be used, for ablating the microchannel,for example, CO₂ laser, Er:YAG, Tm:YAG, Tm fiber laser, Er fiber laser,Ho fiber laser, etc. or any other laser type as is well known in the artwhich may match a predetermined operational parameter such as, forexample, optical absorption by tissue and intensity of laser that arestrong enough to ablate small volumes with minimal lateral damage. Thelaser emitting device 3 may therefore be adapted for emitting anablative laser beam 4 having any suitable power level and/or spot sizeand/or other associated characteristics. The laser power level mayrange, for example, in the range from about 0.5 mJ to about 250 mJ. Thespot size of the laser beam 4 on the tissue surface may range, forexample, in the range from about 10 μm to about 50 μm. For example, aCO₂ laser may use a spot size ranging from about 80 μm to about 150 μmfor ablative treatment and preferably about 80 μm.

In some embodiments of the present invention, the ablation may beproduced by a continuous wave laser, by a single pulse of a laser, or bya series of pulses. The selection of these forms may depend, forexample, upon the depth of the microchannel required, the diameter ofthe microchannel, as well as the size of the thermal affected zone, thatis, the width of the lateral damage. In an embodiment using a continuouswave laser, for example, an ablating laser operating in a wavelength of10.6 nm, the laser emitting device 3 may be operated at a power levelof, e.g., in the range from about 1.0 W to about 250 W for a durationof, e.g., in the range from about 0.02 msec to about 500 msec. In anembodiment using a pulsed CO₂ laser, for example, a series of, forexample, 10 pulses, each having a duration of, for example in the rangefrom about 0.05 msec to about 100 msec may be fired at an energy levelof, e.g. in the range from about 0.2 mJ to about 20 mJ. In an embodimentusing a pulsed laser, a series of pulses, each having a duration of fromabout 0.05 msec to about 100 msec may be fired may be fired at an energylevel of in the range from about 0.2 mJ to about 20 mJ. In skin, forexample, applying a pulsed laser as indicated above may result in amicrochannel 6 of a diameter in the range of from about 80 μm to about100 μm, a depth in the range of from about 300 μm to about 500 μm, and athermal affected zone of lateral width in the range of from about 20 μmto about 300 μm. Additionally, as described below in an embodiment ofthe invention, a series of pulses, of pulsed laser may be fired at thetissue 5 to further deepen the microchannel 6, created as identifiedabove. The microchannel 6 may be deepened to a desired depth, preferablyto the level of the tissue to be non-ablatively treated. It should benoted that the diameter of the deepened microchannel 6 may be in thesame range or different range as the previously created microchannel inthe same location.

In some embodiments of the invention, the microablation channel 6 may besculpted by employing different pulse characteristics of the laser beam.Pulse characteristics of a laser beam, e.g. laser beam 4, may furtherinclude different energy profiles. As mentioned above, the depth h ofthe microchannel and the resulting width of lateral damage and theprofile of the thermal affected zone 7 may be controlled by differentlaser beam characteristics. For example, the laser beam 4 may havecharacteristics resulting in the thermal affected zone 7 having asubstantially constant width (linear profile) 7. It will be recognizedthat some embodiments of the invention may have a thermal affected zone7 profile different from the one depicted in FIG. 1. Furthermore, it isnow possible to produce a microchannel 6 according to embodiments of thepresent invention with a minimal thermal affected zone 7, e.g. a widthin the range from about 1 μm to about 5 μm with the use of the Er:YAGlaser.

In some embodiments of the present invention, the laser unit 2 mayinclude a controller 12 able to control the laser emitting device 3, andan input interface 13 capable of receiving input parameters from user ofsystem 1. Such input parameters may be for defining microablationtreatment parameters, for example. User input parameters to theinterface 13 may further include the microchannel depth, the spatiallocation of the microchannel 6 on the tissue surface 1, etc. Parametersmay be provided at the input interface 13 by an operator of the system,for example, a physician, or alternatively, through an imager programdetailed below. The controller 12 may be able to perform at least one ofthe following functions, as will be described in more detail below: (a)identifying at least one location for treatment; (b) selectingtreatment(s) for each of at least one location; (c) operating a laserand directing mechanism to produce the at least one microablation; and(d) delivering the selected treatment(s) at the at least one site.

Reference is now made to FIGS. 2A, 2B, 2C, and 2D which schematicallyillustrate sequential stages of microablation and treatment inaccordance with an embodiment of the invention. According to anembodiment of the invention, it may be desirable to apply treatment totissue which may be, for example, in the hypodermis 10 in a way thatsubstantially maintains the profile of the thermal affected zonethroughout the treatment protocol. As it is desirable to minimize thenecrosis of tissue at the surface 11, it may be beneficial to apply aplurality of laser pulses onto the tissue 5 in order to reach a depth oftreatment area in the hypodermis 10. As illustrated in FIG. 2A, themicrochannel 6 created by a first ablative laser pulse, may have thedesired thermal affected zone 7, e.g. linear profile of constant width,for example, a minimal width, and may have a depth of h1 that is notsufficiently deep to provide treatment to the hypodermis 10. A secondablative laser pulse may be applied through microchannel 6 of FIG. 2A todeepen the microchannel 6 having a minimal thermal affected zone to adepth h2 into, for example, the dermis 9 of the tissue 5, whilemaintaining the predetermined minimal thermal affected zone profile, asillustrated in FIG. 2B. Finally, as indicated in FIG. 2C, a thirdablative laser pulse may be applied through the microchannel 6 of FIG.2B to deepen the microchannel 6 having a minimal thermal affected zone 7further to a depth h3 into the targeted hypodermis layer 10, whilemaintaining the predetermined thermal affected zone profile 7.Alternatively, if a non-ablative pulse is applied after the profiledepicted in FIG. 2B, the profile may appear as depicted in FIG. 2D.

According to some embodiments of the invention, a delay representing aminimum time, e.g. 1 to 100 msec, may pass between each laser pulse,thereby allowing relevant portions of tissue 5 to cool down between eachpulse. This delay may be between any succession of laser pulses whetherthey are ablative or non-ablative. It is preferable to have a delayafter an ablative laser pulse. To allow for cooling of tissue 5, theminimum time between pulses may be determined according to, for example,a predetermined tissue relaxation time which may define, e.g. the timerequired to dissipate a certain amount of heat absorbed by, e.g. thetissue 5, during a laser pulse applied by the laser device 3. The delaymay also allow venting of ablative tissue and or gases that may havedeveloped during an ablative pulse of light. Accordingly, if a time ofan applied pulse is shorter than the tissue relaxation time and the beamhas a top hat profile a very low amount of heat may dissipate throughwalls of the microchannel 6.

A beam profile that would conform to an inverted top bat may bepreferable in some embodiments of the present invention for forming achannel with well defined side walls, minimal microchannel diameter, anda minimal thermal affected zone. Typically, a beam has a Gaussian powerdistribution across the diameter of its spot. Since the power on theedges of such a spot is less than the power in the center of the spot,it is often difficult to form a straight walled channel or hole. Byhaving a beam profile that has a uniform power distribution across itsspot (a top hat profile) it will be easier to form a straight walledchannel.

In some embodiments of the invention, upon producing the microchanneland clearing a path to the treatment site, a wide variety of types oftreatment may be delivered to the site, as detailed below. In someembodiments, the treatment may be non-ablative laser treatment. Suchnon-ablative laser treatment may be used, for example, for remodelingcollagen. As is more particularly illustrated in FIG. 2D, a non-ablativelaser treatment may be delivered to the tissue 5 in the dermis 9 afterthe microchannel 6 has been created. The path created for thenon-ablative heating of the target tissue may follow embodiments of theinvention detailed above regarding FIGS. 2A, or 2B and/or 2C. That is,heating of subsurface tissue by a non-ablative laser through the createdmicrochannel may be through a microchannel that was created by one or bymore that one ablative pulses. Laser treatment by the laser beam 4 maybe applied to the tissue 5 in the dermis 9, whereby the tissue 5 isheated to a temperature below that at which the tissue is ablated thoughheated to a temperature sufficient to denature collagen, for example, inthe range of from about 50° C. to about 67° C. The non-ablative laserbeam 4 may further create a thermal affected zone of denatured collagen17, without tissue ablation, whereby collagen is heated. The collagenthereupon contracts, thus removing wrinkles. The non-ablative laser beam4 may further be applied to targeted tissue for removing pigmentation,treating blood vessels, and other treatments, as is well known to thoseskilled in the art.

Accordingly, it will be appreciated that the use of the microchannel 6of the present invention as a conduit for applying non-ablative heat totargeted subsurface tissue, enables the heating of the subsurface tissueto be treated without excessively damaging non-targeted tissue, forexample, the surface tissue. Further, the thermal affected zone may beadditionally controlled by having non-ablative heating applicationsinterposed between ablative treatments for creating a larger thermalaffected zone 17 deep in the tissue, for example in the dermis 9.

Reference is now additionally made to FIGS. 3A, 3B, 3C, and 3D whichschematically illustrate sequential stages of treatment in microablationchannels in accordance with embodiments of the invention. In accordancewith to some embodiments of the invention, it may be desirable to createa predetermined non-uniform thermal affected zone profile and/or lateralwidth damaged area along the depth of the channel. In other embodimentsof the invention, an area of tissue in the dermis 9 may be, treated forforming a predetermined thermal affected zone having a profile differentfrom the profile of the thermal affected zone in the epidermis 8 nearthe surface. As is more particularly illustrated in FIG. 3A, themicrochannel 6 having a predetermined thermal affected zone and/orprofile 7 a and a depth h1 may be created by a first ablative laserpulse. As illustrated in FIG. 2D, a second laser non-ablative laserpulse may heat the bottom of the microchannel 6 thereby damaging aspherical area surrounding the bottom of the channel to a depth h3,reaching for example, beyond the dermis 9. This second pulse may havedifferent characteristics than the first pulse, producing a thermalaffected zone having a different area and/or profile than the firstpulse and resulting in the profile illustrated in FIG. 2D. When a secondablative laser pulse (that is, the third pulse to this treatment area)is applied through the damaged tissue on the bottom of the microchannel,a profile 7 b as depicted in FIG. 3B is formed. Thus, FIG. 3B depicts anablative laser pulse applied subsequent to the non-ablative laser pulsewhich formed the profile depicted in FIG. 2D. Alternating ablative lasertreatment with non-ablative laser treatment may result, for example, ina microchannel having a thermal affected profile as illustrated in FIG.3C. It will be understood that a microchannel may be produced to anydepth and by any number of pulses for creating a series of predeterminedthermal affected zones that may vary along the depth of themicrochannel. In this way, a predetermined thermal affected zone profilealong the microchannel 6 is formed. It is thus possible to build avariety of predetermined thermal affected zone areas and/or profilesalong the wall and/or the bottom of the microablated channel, using asequence of pulses with different parameters (e.g. energy and durationor wavelength) and employing the natural thermal conductivity of tissue.For example, in another embodiment of the invention, an ablative laserpulse applied to the tissue 5 may have characteristics producing athermal affected zone having an area and/or profile 7 d as illustratedin FIG. 3D. The thermal affected zone 7 d in FIG. 3D illustrates thatthe thermal affected zone area may decrease along the depth of thechannel, according to predetermined laser beam parameters. Of course,once the depth of the tissue targeted for treatment is reached, thenon-ablative heating of the tissue should preferably commence.

In some embodiments of the present invention, the creation of themicrochannel 6 with the desired thermal affected zone profile 7 alongthe walls and/or bottom of the microchannel 6 may itself be the desiredtreatment method. Additionally or alternatively, creating themicrochannel 6 itself may facilitate the desired treatment method, byproviding access directly to a subcutaneous site for treatment. Forexample, upon completion of the microchannel, a substance may bedelivered to the treatment site by any means, including for example,ultrasonic delivery. Additionally or alternatively, the microchannel mayserve as a conduit for transdermal substance delivery, for example, fordiffusion, electrophoresis, ointments, acids, healing substances,chemical peeling agents, collagen modification agents, fillers, stemcells, or any variety of administering medicines and the like. It willbe noted that the depth of the microchannel need not be the only or eventhe primary treatment site; rather the treatment site may be any and allsites along the walls and/or bottom of the microchannel adjacent to orproximate the microchannel.

In some embodiments of the invention, the controller 12 may provide 3 acommand via a signal 14 to the laser device for applying a pulse orseries of pulses to the tissue 5. The controller may provide a varietyof commands to the laser device 3, for example, the sequence andduration of pulses to apply to the tissue 5. The controller may alsoselect form a variety of laser sources for applying a desired sequenceof ablative and non-ablative laser applications to a particular site.The controller may also prescribe the desired delay between the laserapplications. Furthermore, the controller 12 enables the laser emittingdevice 3 to deliver precise multi-spot ablation to selective portions oftissue in accordance with preselected treatment protocols as is wellknown by the physician.

In some embodiments, more than one microchannel may be producedsubstantially concurrently or in rapid sequence on the tissue 5, forexample, by directing the laser emitting device 3 from one predeterminedsite to another of the tissue 5, applying a pulse at each site andreturning precisely to the previously treated site so as to apply thenext pulse in the sequence. Thus, while the tissue 5 at one microchannelis cooling, the controller 12 may send a command to the laser device 3to move among one or more sites on the tissue 5 for creating a pluralityof microchannels at a plurality of sites. Such a device may use, forexample, a laser scanner. Such scanners may operate in accordance withthe teachings in U.S. Pat. Nos. 5,713,902; 5,957,915; and 6,328,733, allof which are incorporated herein by reference. For example, at a firstscanning sequence, the laser device 3 may provide the laser beam 4 onthe first site resulting in a microchannel of depth hl. The controller12 may then move the laser device 3 to a second site to produce thereona microchannel having a depth h1. This process may continue until thelaser device 3 performed on each location has a microchannel resultingin depth h1. The controller 12 may then proceed to provide the laserbeam 4 on a microchannel site further ablating a microchannel resultingin another microchannel of depth h2 directly below the firstmicrochannel site. Alternatively, the second laser application may be anon-ablative laser beam. The controller 12 may then move the laserdevice 3 to a second site to produce a microchannel of depth h2. Thisprocess may continue until the laser device 3 performed on eachmicrochannel location of depth h1 a second laser beam pulse resulting ina microchannel of depth h2. Of course, the order of the second beamacross the selected treatment sites may be in a different order orsequence than the first pass. Alternative scanning sequences may applylaser beam pulses repeatedly at a location, then moving to anotherlocation to apply laser pulses. It may not be necessary that the sameseries of pulses (characteristics including duration and power) beapplied at each location in the sequence and any number of series ofpulses may be applied to tissue at various locations.

In some embodiments of the invention, the tissue 5 may be manipulatedand the laser emitting device 3 positioned for applying the laser beam 4to the tissue 5. For example, the skin tissue to be treated may belifted and the laser beam 4 may be applied from the side. Furthermore,the controller 12 may direct the laser emitting device 3 to apply thelaser beam 3 to the tissue 5 from a variety of angles from theperpendicular.

In another embodiment of the invention, it may be desirable to increasethe amount of radiation per unit of surface area of the tissue 5. Forexample, the tissue 5 may be stretched prior to applying laser beam 4 tothe tissue. Referring to FIG. 4A, laser beam 4 may be applied tounstretched tissue 5 over a surface area 19 of tissue. The tissue 5 maybe stretched in a variety of directions as selected by the physician,for example, the lateral direction, manually or by some device applyinga stretch 20, prior to producing the microchannel 6 as detailed above inan embodiment of the invention. Referring to FIG. 4B, applying stretch20 to the tissue 5, effectively increases the amount of radiation perunit surface area 19 of the tissue 5. The microchannel 6 (FIG. 4C)created in the stretched tissue 5 will possess dimensions andcharacteristics as detailed above. Release of the tissue stretch 13, mayresult in a relaxed tissue 5 wherein the microchannel 6 now possesses asmaller diameter D′ (i.e. D′<D; Ref. FIG. 4D). The reduction inmicrochannel diameter may also be a function of tissue properties, forexample, tissue elasticity, tissue hydrated conditions, and thethickness of the stratum corneum. Thus, by stretching the skin prior toa laser beam is applied, the area of damaged skin may be furtherreduced. Stretching the skin has many advantages beyond just minimizingthe amount of damaged skin. For example, by stretching the skin duringthe application of an ablative laser for creating a microchannel, thediameter of the microchannel will be further reduced. In this way,infection has a smaller entrance point and the chance for infection maybe further minimized. Stretching the skin during the application of thelaser beam (both an ablative laser beam and a non-ablative laser beam)provides additional advantages, for example, better penetration, betterevacuation of vapors, and being less sensitive to the position of thetarget relative to the applied beam.

The system may also include an imager to enable a user to view thetissue area and to choose a treatment site. For example, the imager andan image processor may be used to determine the wrinkle topology of atissue. For example, by using the imager combined with the applicationof polarized light, the outline, depth, and profile of the skin'stopology may be more precisely determined. The wrinkle topology may beprovided to the input interface 13 to communicate with the controller 12and send a signal 14 to the laser device 3 to maximize the aim of thelaser device 3 to the target tissue 5. The wrinkle topology may be usedto measure the effectiveness of the treatment as well as used foridentifying targeted sites that may require additional treatment.

An imager may also be used to generate optical feedback, either manuallyto the eye of the user, or automatically to an image processor, in orderto return the laser to a previously treated site. The processor mayprocess the image obtained from the imager for providing information tothe controller for varying the treatment locations, the particular laserto be used, the laser spot size, the spot location, etc. In this manner,if the patient moved between pulses, an imager and processor may enablereturning the laser to the precise site of the previous pulse. Use of animager to optically track or determine tissue position may be used inconcert with the process described above of the sequential creation ofmicrochannels, as is well known to those skilled in the art.

As shown in FIG. 5, in another embodiment of the invention, themicrochannel may be used to facilitate treatment to subcutaneous tissueby a means other than through the microchannel itself. The void of themicrochannel may act as a barrier, or insulating separation of air,between layers of tissue on either side of the microchannel. Therefore,a microchannel may be used in conjunction with radio frequency (RF)energy treatment to allow driving a current below the microchannel. Asillustrated, the microchannel 6 is created according to an embodiment ofthe present invention detailed above, having a width W, a length L, anda depth h. In this embodiment, the microchannel depth h reaches into thedermis of the tissue and the targeted tissue is beneath the microchannel6 in the dermis 9. Radio frequency electrodes 15 and 16 may be appliedto the tissue at opposite sides of the microchannel 6. When RF current18 is applied, the insulating (non-conducting) property of themicrochannel 6 requires the current to flow between electrodes 15 and16, below the microchannel depth h, directing the current to deepertissue than would have occurred in the absence of the microchannel 6.The length L of the microchannel should preferably be at least twice itsdepth (2D) so that the applied current may go through the targetedtissue and not find an alternate path of less resistance. The length ofthe microchannel in this embodiment of the invention may be in the rangeof from about 100 μm to about 500 μm and preferably about 300 μm.Accordingly, it will be appreciated that by using the microchannels ofthe present invention, the heating of deeper layers of tissue may beachieved without damaging the surface tissue. It will further beappreciated that controlling the dimensions of the microchannel, e.g.,the depth, width, and/or length of the microchannels may define thetreatment provided by the treatment device, e.g., the RF electrodes, tothe treatment layer of the tissue. It will be noted that byconcentrating the current, the microchannel may provide for increasedcurrent density at the desired treatment site. A similar approach may beused for heating and followed shrinkage of collagen fibers at apredetermined depth.

Creating a microchannel into the tissue for reaching an area of targetedtreatment may also be achieved without an ablative laser. For example, amicrochannel may be created mechanically with a heated microneedle.After the microchannel is thus formed, non-ablative treatment may beapplied

Reference is now made to FIG. 6, which schematically illustrates aflow-chart of a method for performing micro-ablation on a tissue inaccordance with an embodiment of the invention. As indicated at block601, the method may include, for example, positioning the laser devicefor performing microchannel ablation. For example, the user of thesystem 1 may initially position the laser device 3 relative to the skin5 to enable creating the microchannel at a desired location. Asindicated at block 602, the method may also include, for example,determining the depth of the microchannel. For example, the user maydetermine that the desired depth of the microchannel 6 (FIGS. 2A, 2B and2C) is h3. As indicated at block 603, the method may also include, forexample, determining the width of the microchannel and/or the thermalaffected zone. For example, the user may determine that the desiredwidth of the microchannel 6 is D (FIG. 1) and the desired thermalaffected zone profile may vary as in 7 a, 7 b, 7 c, and 7 d (FIGS. 3A,3B, 3C and 3D). The density of microchannels (e.g., number of channelsper area) can also be determined. The wavelength for the differentstages of the ablation may also be determined. As indicated at block604, the method may also include, for example, producing a microchannel.For example, the laser device 3 may emit a laser beam and may therebyproduce the microchannel 6 in the tissue 5. As indicated at block 605,the method may also include, for example, applying treatment onto amicrochannel location. For example, applying heat treatment to affectcollagen at bottom of microchannel 6 (FIG. 2D). It will be recognizedthat the step of applying treatment is optional and need not bepracticed in every embodiment of the invention.

FIG. 7 depicts a flow chart method in accordance with embodiments of thepresent invention. At block 700, the orientation of the tissue 5 isselected for treatment, the tissue, e.g. skin is stretched, lifted, orleft natural. At block 701, image analysis of the tissue surface isperformed, for example, to create wrinkle topology, to provideinformation to the controller 12 (FIG. 1) in order to maximize laserorientation. It will be recognized that the step of image analysis isoptional and need not be practiced in every embodiment of the invention.At blocks 702 and 703, the depth and width of the microchannels may bedetermined respectively, for example, based on the treatment programselected or selected by the operator. At block 704, the thermal affectedzone (e.g. area and/or diameter of necrosis) may be determined, forexample, by setting the pulse duration, pulse energy, the number ofpulses, or the density of the pulses based on the treatment program, orbased on selection by the operator. At block 705, the area of collagenshrinkage (i.e. thermal affected zone 17) may be determined (FIG. 2D).At block 706, a treatment pattern or program may be determined, forexample, by the operator of the device selecting an appropriate program.At block 707, the size of the microchannel pattern may be determined,for example, automatically by scanning, or based on the treatmentprogram, or by an operator selecting the appropriate pattern size. Atblock 708, the fill factor, for example, the density of themicrochannels on the tissue, may be determined, for example,automatically by the device, e.g., based on the treatment program, or byselection by the operator of the device. At block 709, the device may bepositioned on the tissue, and at block 710, the treatment may beperformed by forming the microchannels, and/or applying any otherdesired treatment.

Add

In a further aspect of the invention, systems are provided for controlof the lasers used in microablation. As is well known lasers comprise alaser medium, a pumping system to generate a population inversion in themedium, and optics to pass certain photons repeatedly through the mediumand to allow a usually narrow beam of light to exit the medium. Thepumping system may be, for example, a set of electrodes and associatedcontrols which create a glow discharge in a gas by supplying DC or RFenergy to the gas, with the discharge producing a population inversion.For background on lasers see generally Jeff Hecht, Laser Guidebook (2nded. 1992) and Orazio Svelto, Principles of Lasers (David Hanna trans.4th ed. 1998).

In systems for laser microablation one may advantageously, for example,a CO₂ laser in which initiation of laser action produces a high opticalpower output pulse, for example having a peak output power of 300 W. Anexemplary optical power output of such a system over time is shown inFIG. 8. Lasers having pulsed optical output suitable for lasermicroablation have been marketed by the assignee of this application,for example, under the name UltraPulse®. The assignee's laser productsinclude RF excited slab CO₂ lasers of the waveguide type.

In existing systems for laser microablation it is common to present theuser (normally a physician) with an interface whereby the user choosesan output energy. This energy may, for example, be on the order of tensof millijoules, for example in the range of about 5 mJ to about 50 mJ.

A microablation system could provide the desired number of millijoulesin the following manner. As part of the system design, one determines acurve of the light power output over time of the laser when apredetermined voltage step waveform is applied to the pumping system. Onthe basis of that curve, for a series of time values t one calculatesthe area under the curve from time 0 (onset of voltage applied topumping system) to time t. That area under the curve will represent theamount of light energy that the system will output if started at time 0and shut down at time t. From the series of areas under the curve fortime values t, one can calculate by interpolation for any desired energyoutput a time value which will produce that energy output. Thus, for anyenergy, the system can calculate how long to apply power to the pumpingsystem to produce that energy.

Alternatively, the system could start the application of energy to thepumping system and measure the light output power of the system. Thesystem could integrate the light power output of the system over time(e.g., using some numerical integration algorithm) and turn off theenergy input to the pumping system when the integrated power sinceturn-on reaches the desired energy level. The system might take intoaccount the turn-off transient of the light power output when thepumping system shuts down and so shut down slightly short of the desiredenergy to compensate for that transient.

It is desirable to extend the capability of such systems whereby theuser chooses both a desired amount of light energy and a duration overwhich the energy is applied. With this capability, the system describedabove based on the integrated optical power output would potentially notbe adequate because it might have to stop short of the user's selectedduration in order to meet the total energy constraint.

It is therefore desirable to have the ability to reduce reliably theoutput light energy level of the laser being used, even when it employsa roughly fixed input energy level to the pumping system and has aroughly fixed light power output curve as a function of time when thatfixed input energy level is applied to the pumping system.

Given the curve of output light energy versus time described above, thesystem can calculate the degree of attenuation necessary to achieve boththe desired energy output and the desired duration of action t. Thesystem can, for example, determine the duration t_(full) to produce thedesired energy output without attenuation, and then attenuate byt_(full)/t to deliver the desired energy output over the choseninterval.

There are a number of reasons why the user of a laser microablationsystem would want to be able to vary the duration as well as the energydelivered by the system. One important reason is that a longer durationadministration of the same energy can have quite different effects ontissue. As discussed above, there is in tissue both ablative andnon-ablative damage. A rough differentiation between these two types ofdamage can be made according to whether the tissue temperature reachesthe boiling point of water, in which case the damage in portions oftissue where that occurs would be ablative. Because heat is conductedaway from the area where the relatively thin laser beam enters tissue,if the energy is being applied more slowly the tissue will not reach theboiling point of water and the damage will tend to be non-ablative. Asdiscussed above and depicted in FIGS. 1-5, where non-ablative damageoccurs it will tend also to have a different shape which may be moredesirable in achieving the desired effect on tissue.

In addition to varying the duration during which the optical power isapplied, control over the optical power may also be used to applyinitially the normal high power pulse of optical energy which the lasernatively produces, followed by a selected period of sub-ablation energy.The sub-ablation energy as discussed above produces a different kind ofalteration of tissue from the initial pulse. This alteration is referredto sometimes as “coagulation.” The ability to choose a particular powerlevel and duration following the initial high power pulse opens the wayto a much more precise control of the non-ablative damage.

For cosmetic purposes, for example, it can be desired to have primarilynon-ablative damage located shortly below the surface of the skin, asschematically depicted for example in FIG. 3C.

It is also possible with control over output optical power to generate,for example, double high-power pulses of optical energy separated by aperiod in which a non-ablative level of optical power is applied.

One method which is possible for controlling the output energy level ofthe laser is to place a set of attenuators at the output of the laser.For example, one could have a set of attenuators which have attenuationvalues of about 10%, about 20%, about 30%, about 40%, about 50%, about60%, about 70%, about 80%, or about 90%. Alternatively, one could havean arrangement in which a smaller number of attenuators is employed withtwo or more attenuators being put in the path of the beam in order toachieve a greater degree of attenuation than what one attenuator canproduce.

A variety of mechanical arrangements may be employed to place anattenuator in the path of the laser beam. For example, referring to FIG.11A, a rotational arrangement 200 may include a shaft (not shown) thatmoves until an attenuator 202 is in place and then moves to take theattenuator 202 out of the path of the laser beam 201. Alternatively, asshown in FIG. 11B, a solenoid-based arrangement 220 may involve linearmotion of an attenuator 204 in the laser beam path 201. With therotational arrangement, a number of different attenuators of differentdegrees of attenuation can be attached to the shaft and the appropriateattenuator rotated into place.

In a system with a fixed set of attenuation percentages, the systemmight for example choose the percentage which is closest to thatcalculated as described above and utilize that percentage.Alternatively, the system might modify the time duration somewhat fromthe desired duration to achieve the exact energy chosen by the user withthat closest feasible attenuation. Alternatively, the system mightchoose the smallest attenuation percentage which is greater than thatcalculated as described above, or the largest attenuation which is lessthan that calculated as described above.

Attenuators for light are known in the art. The precise form andstructure of the attenuator for use with a laser microablation systemwill depend very much on the wavelength of the laser output, becausedifferent materials have different frequency responses over the broadrange of frequencies for which lasers are available. The laser used in alaser microablation system will generally output a fairly narrowwavelength range corresponding to the set of wavelengths of transitionsthat take place as part of the laser action. For example, CO₂ lasersproduce light at wavelengths from about 9 μm to about 11 μm. Thestrongest light output from a CO₂ laser will tend to be at about 10.6μm. The precise form and structure of the attenuator will also depend onthe optical power level being used, for example milliwatts or watts orhundreds of watts, since the attenuator itself should not be altered bythe energy which it is absorbing. For CO₂ and other relatively powerfulinfrared lasers metal screens work well as attenuators.

In addition to attenuators which have a fixed degree of attenuation suchas 60%, it is also possible to employ attenuators that have a degree ofattenuation which is electronically controllable. Commercialacousto-optic and electro-optic modulators 206 are available, forexample.

In an alternative technique for varying both duration and light energyprovided by a laser microablation system, it is possible to turn theenergy of the laser's pumping system on and off repeatedly. For example,in the case of a gas laser system which creates a population inversionby delivering DC or RF electrical energy through electrodes to a gas,the delivery of DC or RF electrical energy can be turned on and offrepeatedly. If the times at which the pumping energy is turned off andthen turned back on are chosen appropriately, it is possible to operatethe laser system at a chosen average optical power output well below thepeak power, e.g., via pulse width modulation. It is possible, forexample, to operate the system between about 1% and about 100% of peakpower, or between about 10% and about 100% of peak power, with opticalpower output being chosen as desired.

The duty cycle applied to the pumping system may vary, for example,between about 20% and about 80%, or between about 40% and about 60%.Frequencies up to about 50 kHz are conveniently employed for turning onand off the pumping system power. FIG. 9 depicts schematically how onecan control optical output power by turning the pumping system power onand off In that figure we see in dashed lines the initial transient asdepicted in FIG. 8. We also see above the pumping system power as it isturned on and off. We see the resulting system optical output poweroscillating around a power level substantially lower than the peak.

FIG. 10 depicts the use of pumping system power control to applyinitially the normal high power pulse of optical energy which the lasernatively produces, followed by a selected period of sub-ablation energy.We see that the pumping system energy is initially turned on and held onso that the normal high power pulse is produced. After a period of time,the periodic turning on and off begins so as to produce the period ofsub-ablation energy.

There are various ways to decide when to turn the pumping power on andoff in order to produce a desired optical output power. With equipmentin place for measuring the optical output power of the system, it wouldbe possible to use a feedback loop in which, for example, the times ofthe on-off and off-on transitions in the pumping system power are variedin order to maintain the average light power output close to the preciselevel desired, or for other control purposes. Any of a wide variety offeedback control algorithms known to persons of skill in the art may beemployed. Reference may be made, for example, to Gene Franklin et al.,Feedback Control of Dynamic Systems (6th ed. 2009). Control could be,for example, a simple thermostat-like control in which power to thepumping system is turned off when instantaneous output optical powerexceeds the desired level plus a percentage, and turned back on wheninstantaneous output optical power falls below the desired level plus apercentage. More complicated feedback controls in which, for example,the total energy delivered so far is computed and influences thedecision to turn the power to the pumping system on or off may also beemployed.

One may, alternatively, simply choose empirically the first turn-offtime and the duty cycle to achieve each of a range of desired opticaloutput powers with the laser in a particular system or withrepresentative such lasers, and then program those times and duty cyclesinto the system's electronics for subsequent use in the field.Alternatively, one might use a measured transient output power waveformin response to an energy square wave applied to the pumping system. Thismeasurement will produce a turn-on transient waveform and a turn offtransient waveform. These waveforms may be characterized, for example,by time constants. For the turn-off transient, the time constant mightbe, for example, the time required for the waveform to fall to ½ of itsoriginal value. One could assume that, with on-off control of thepumping system input, the transient after the first turn-off will followthe measured turn-off transient and the transient after the firstturn-on will follow the measured turn-on transient, and so choose afirst turn-off time and duty cycle such that the output power predictedwith the assumption will oscillate around a desired output power.

With the use of on-off driving of the pumping system power as describedabove, it is possible that there would be substantial fluctuation in theoutput power of the laser about the desired average power. Suchfluctuation is generally not problematic in applications involvingtissue ablation, since the thermal time constant of tissue isapproximately 1 ms, and so fluctuations above approximately 1 kHz do nothave a significant thermal effect.

Nonetheless, if it is desired to reduce fluctuations in the opticalpower output when using on-off driving of the pumping system, one way toachieve this would be to increase the frequency of the on-off drivingwaveform, reducing the ripple in the optical power output.

EXAMPLE

It is to be understood that the following example of the presentinvention is not intended to restrict the present invention since manymore modifications may be made within the scope of the claims withoutdeparting from the spirit thereof.

A study was conducted that consisted of two research criteria. The firstcriterion evaluated different laser energy doses on 47 consecutivesamples of skin. The doses ranged from 5 m.T to 200 mJ. The width anddepth of the ablated “column” was measured as well as the surroundingwidth and depth of necrosis. The second criterion compared the effectsof doses ranging from 5 mJ to 20 mJ on the arms of selected volunteers.These evaluations were recorded immediately after the firing of thelaser; at one hour; one day and four days.

SUMMARY OF RESULTS OR FINDINGS

The depth and diameter of the ablated columns correlated in a linearfashion with the dose. The column depth could be directly controlled andranged from 180 to 1378 microns, depending on the dose level. Despitethe wide range of dosing parameters, the column diameter was tightlyconfined and only ranged from 34-106 microns with most of columndiameters being in the 50-70 micron range. Necrosis depth ranged from27-213 microns. Necrosis width was extremely confined and ranged onlyfrom 19-55 microns. Histologically, the ablated columns produced by 5 mJand 10 mJ pulses reached the mid- to deep-dermis; columns onlypenetrated to the fat at the highest dose (200 mJ). On doses of 5, 10,and 20 mJ, the resultant skin erythema and edema was evident at 1-2days, but the mild to moderate erythema faded by the fourth day. Therewere no cases of necrosis.

CONCLUSIONS REACHED

Utilizing histologic evaluation, it is a novel carbon dioxide basedmicroablation device can produce selective digital injury to dermalcollagen using very low energy levels. The collateral necrosis is verylimited. Preliminary clinical evaluation using low energy dosesdemonstrates mild to moderate erythema that fades at four days. Thesefindings will be used to determine the dosing for future clinicalstudies.

Although the particular embodiments shown and described above will proveto be useful in many applications in the skin treatment art to which thepresent invention pertains, further modifications of the presentinvention will occur to persons skilled in the art. All suchmodifications are deemed to be within the scope and spirit of thepresent invention as defined by the appended claims.

Example 1

It is to be understood that the following example of the invention isnot intended to restrict or to limit the invention because many moremodifications may be made within the scope of the claims withoutdeparting from the spirit thereof.

A study was conducted that consisted of two research criteria. The firstcriterion evaluated different laser energy doses on 47 consecutivesamples of skin. The doses ranged from 5 mJ to 200 mJ. The width anddepth of the ablated “column” was measured as well as the surroundingwidth and depth of necrosis. The second criterion compared the effectsof doses ranging from 5 mJ to 20 mJ on the arms of selected volunteers.These evaluations were recorded immediately after the firing of thelaser; at one hour; one day and four days.

SUMMARY OF RESULTS OR FINDINGS

The depth and diameter of the ablated columns correlated in a linearfashion with the dose. The column depth could be directly controlled andranged from 180 to 1378 microns, depending on the dose level. Despitethe wide range of dosing parameters, the column diameter was tightlyconfined and only ranged from 34-106 microns with most of columndiameters being in the 50-70 micron range. Necrosis depth ranged from27-213 microns. Necrosis width was extremely confined and ranged onlyfrom 19-55 microns. Histologically, the ablated columns produced by 5 mJand 10 mJ pulses reached the mid- to deep-dermis; columns onlypenetrated to the fat at the highest dose (200 mJ). On doses of 5, 10,and 20 mJ, the resultant skin erythema and edema was evident at 1-2days, but the mild to moderate erythema faded by the fourth day. Therewere no cases of necrosis.

CONCLUSIONS REACHED

Utilizing histologic evaluation, it is a novel carbon dioxide basedmicroablation device can produce selective digital injury to dermalcollagen using very low energy levels. The collateral necrosis is verylimited. Preliminary clinical evaluation using low energy dosesdemonstrates mild to moderate erythema that fades at four days. Thesefindings will be used to determine the dosing for future clinicalstudies.

Although the particular embodiments shown and described above will proveto be useful in many applications in the skin treatment art to which thepresent invention pertains, further modifications of the presentinvention will occur to persons skilled in the art. All suchmodifications are deemed to be within the scope and spirit of thepresent invention as defined by the appended claims.

Example 2

The following descriptions of the invention are provided as illustrativeexamples only and are not intended to limit or to restrict theinvention. It is to be understood that the following examples of theinvention are not intended to restrict or to limit the invention becausemany more modifications may be made within the scope of the claimswithout departing from the spirit thereof.

Referring to FIGS. 12A-12F, a demonstration of the “pulse widthmodulation” techniques is described and FIGS. 12A-12F provide graphsillustrating laser output responses to control inputs. By modulating thecontrol to the laser, one can turn the pumping system on and off,turning a high power CO2 laser into a low average power laser. A labdemonstration was constructed with different pulse train structures todemonstrate different modulated laser output profiles which may resultin a controlled thermal response. FIG. 12A illustrates a typical outputof a high powered CO2 laser. The upper waveform, identified as #1 in thegraph, is the control input and the lower waveform, identified as # 2 inthe graph, is the laser output. The high power nature of the laseroutput to a typical control is shown.

With this waveform, one would expect the thermal response depicted inFIG. 1.

The graph of FIG. 12B shows a typical output of a high powered CO2 laserwith a modulated control resulting in a low average power output. Theupper waveform, labeled #1 in the graph, is the control input and thelower waveform, labeled #2 in the graph, is the laser output. The lowpower nature of the laser output to this modulated control is shown.With this waveform, one would expect the thermal response depicted inFIG. 2A.

FIG. 12C illustrates a graph that shows an output of a high powered CO2laser. The upper waveform, labeled #1 in the graph, is the control inputand the lower waveform, labeled #2 in the graph, is the laser output.This graph shows the variable nature of the pulse shape due to thecontrol modulation of varying duty cycles and duration. The high powerexposure of the laser output followed with a low power exposure isshown. With this waveform one would expect the thermal response depictedin FIG. 2D.

The graph of FIG. 12D shows the output of a high powered CO2 laser. Theupper waveform, labeled # 4 in the graph, is the control input and thelower waveform, labeled #1 is the laser output. In this example, thevariable nature of the pulse shape due to the control modulation ofvarying duty cycles and duration is illustrated. In contrast to FIG.12C, the low power exposure of the laser output followed with a highpower exposure is shown. With this waveform one would expect the thermalresponse depicted in FIG. 2B.

FIG. 12E illustrates a graph indicating one of the more unique outputsof a modulated high powered CO2 laser. The upper waveform, labeled #4 inthe graph, is the control input and the lower waveform, labeled #1 isthe laser output. In this example, the variable nature of the pulseshape due to the control modulation of varying duty cycles and durationis shown. The high power exposure of the laser output is followed with alow power exposure and followed with another high power exposure. Withthis waveform one would expect the thermal response depicted in FIG. 3B.

The graph of FIG. 12F shows one of the more unique outputs of amodulated high powered CO2 laser. The upper waveform, labeled #4 in thegraph, is the control input and the lower waveform, labeled #1 is thelaser output. In this example, one can see the variable nature of thepulse shape due to the control modulation of varying duty cycles andduration. The high power exposure of the laser output is followed with alow power exposure and followed with another high power exposurefollowed with another low power exposure. With this waveform one wouldexpect the thermal response depicted in FIG. 3C.

Example 3

The following description of the invention is provided as anillustrative example only and is not intended to limit or to restrictthe invention. It is to be understood that the following example of theinvention is not intended to restrict or to limit the invention becausemany more modifications may be made within the scope of the claimswithout departing from the spirit thereof.

Referring to FIG. 12, an experiment was performed, demonstrating theeffect of pulse duration and peak power on the tissue response. Threeexposures of equal energy, equal spot size, but differing pulse durationwere exposed into a polyacrylide gel, containing a high concentration ofthe target water chromophore. Left is shortest pulse (20 us), middle isa medium pulse (300 us), and right is longest pulse (1000 us). FIG. 13demonstrates the varying depth of ablation and additional lateralthermal damage of the lower power exposures.

CONCLUSIONS REACHED

High power exposures translate to deep ablation capabilities, while lowpower exposures ablate less and leave more thermal damage. One mayconclude that, if combining low and high power combinations, one canachieve thermal damage deeper and/or vary the thermal damage zones for amultitude of depths.

Referring to FIG. 14, in a further aspect the invention provides amethod 300 for treating tissue using a laser system with pulsed lightoutput, as described above. The method 300, however, is exemplary onlyand not limiting. The method 300 may be altered, e.g., by having stagesadded, removed or rearranged.

At phase 302, the method includes selecting at least two of: (i) adesired total light output energy, (ii) a desired average light outputpower, or (iii) a desired duration of laser application.

At phase 304, the method further includes controlling the laser by thesystem in order to achieve the selected conditions (i), (ii), or (iii)specified by the user.

At phase 306, the method includes directing the light output of thelaser to the tissue to be treated over the desired duration.

At stage 308, the method includes varying a control for power, whichproduces a population inversion, between on and off states, such that, apopulation inversion may be produced when the control is varied from anoff state to an on state.

It will be appreciated by persons of ordinary skill in the art thataccording to some embodiments of the present invention otherapplications according to the principles of the present invention arepossible and are in the scope of this application. While certainfeatures of the invention have been illustrated and described herein,many modifications, substitutions, changes, and equivalents will nowoccur to those of ordinary skill in the art. It is, therefore, to beunderstood that the appended claims are intended to cover all suchmodifications and changes as fall within the true spirit of theinvention.

All patents, patent applications, and publications mentioned herein arehereby incorporated by reference in their entireties. However, where apatent, patent application, or publication containing expressdefinitions is incorporated by reference, those express definitionsshould be understood to apply to the incorporated patent, patentapplication, or publication in which they are found, and not to theremainder of the text of this application, in particular the claims ofthis application.

1. A method for treating tissue using a laser system with pulsed lightoutput, comprising (a) indicating by a user at least two of (a1) adesired total light output energy, (a2) a desired average light outputpower, or (a3) a desired duration of laser application, (b) controllingthe laser by the system in order to achieve the selected conditions(a1), (a2), or (a3) specified by the user, (c) directing the lightoutput of the laser to the tissue to be treated over the desiredduration.
 2. The method of claim 1, wherein the laser system has acontrol for power used to produce a population inversion, wherein thecontrol varies between on and off states, a population inversion beingproduced when the control is varied from an off state to an on state,and wherein the system varies this control between on and off states atleast four times in order to achieve the selected conditions (a1), (a2),or (a3).
 3. The method of claim 1; wherein the laser system has at leasttwo attenuating elements and the system places at least one of these atleast two attenuating elements in the path of the laser's output inorder to achieve the desired energy or average power or duration.
 4. Themethod of claim 1, wherein the light output of the laser is ablativeduring a portion of the time that it is directed to the tissue andnon-ablative during another portion of the time that it is directed tothe tissue.
 5. The method of claim 1, wherein the light output of thelaser is directed to the tissue through a mirror, an optical fiber, aprism, or another optical element.
 6. The method of claim 1, wherein asa result of the light output power being directed to tissue, a channelis ablated in the tissue having a predetermined width and predeterminedheight, and a thermal affected zone of predetermined volume and shape iscreated proximate said channel.
 7. The method of claim 6, wherein thetissue has a surface through which the light output power passes and thethermal affected zone has a cross section in a plane parallel to thatsurface which increases in diameter with the plane's distance from thatsurface, so that the diameter of the cross section increases withdistance from that surface for a range of distances to the surface. 8.The method of claim 6, further comprising administering a treatmentthrough the channel.
 9. The method of claim 1, wherein the output lightpower raises the temperature of at least a portion of the tissue intowhich it is directed above 100° C.
 10. The method of claim 2, whereinthe system measures the laser's light output power.
 11. The method ofclaim 10, wherein the measured light output power is used in a feedbackcontrol system in order to decide when to change the control from an onstate to an off state or vice versa.
 12. The method of claim 1, whereinthe desired average light output power is no greater than about 10% ofthe maximum instantaneous light output power which the laser is capableof producing.
 13. The method of claim 1, wherein the light output powerdeviates by no more than 10% from the desired average light output powerduring at least about 90% of the time that the laser is producing lightoutput in response to the user's setting.
 14. The method of claim 3,wherein the system selects from a set of discrete attenuation values theattenuation closest to the desired level.
 15. A system for treatingtissue with light, comprising: a laser with pulsed light output and adigital controller for the laser, wherein the digital controllerimplements a user interface which permits a user to select at least twoof (a) a total energy to be applied to the tissue, (b) a duration of theapplication of light to the tissue, and (c) a desired average powerlevel to be applied to the tissue, and wherein the digital controllercontrols the laser's light output to achieve the conditions (a), (b), or(c) specified by the user.
 16. The system of claim 15, wherein the lightwith which the tissue is treated has a wavelength of at least about 9μm.
 17. The system of claim 15, wherein the laser is capable ofproducing a pulsed light output with at least about 200 W peak lightpower.
 18. A system for treating tissue with light, comprising: a laserwith pulsed light output, an optical system for directing the lightoutput of the laser to the tissue, and a digital controller for thelaser, wherein the laser comprises a pumping mechanism and a control forthat mechanism which can be varied between an on state and an off state,wherein varying the control from the off state to the on state producesa population inversion, wherein the digital controller is programmed tovary the control from the off state to the on state and back to the offstate a plurality of times, and wherein the light output power of thelaser does not fall to zero between the first transition to the offstate and the last transition to the on state.
 19. The system of claim18, wherein the digital controller is programmed to receive from a userat least one numerical value and to compute from the at least onenumerical value a desired light output power, and wherein the averagelight output power of the laser between the first transition to the offstate and the last transition to the on state lies within about 10% ofthe desired light output power.